Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 221049
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
549 AM CDT Tue Apr 22 2014

.SHORT TERM: (Today through Thursday)
Issued at 348 AM CDT Tue Apr 22 2014

Cold front extending from near Effingham IL southwest to near
West Plains MO. The cooler and drier air is lagging the wind shift
a bit and is just now working into central and eastern Missouri.
Pretty solid ridge behind the front is progged to build southeast
into the Mississippi Valley today. Looking back to yesterday,
highs across northern and eastern Nebraska, southern South Dakota,
and western Iowa ranged from the mid 60s to low 70s. This is
agreeable with latest MOS guidance...but with plenty of sunshine
expected today and the recent trend of MOS to be a little too
cool, I went just a degree or two higher. With wind dropping off
and a clear sky tonight, should see excellent radiational cooling
conditions develop, especially along and east of the Mississippi
River which will be closest to the ridge axis. MOS guidance is
pretty uniformly in the 40 to 45 degree range for lows tonight,
but would not be surprised to see some of our cold spots drop into
the upper 30s.

Should see the wind turn back around to the southeast on Wednesday
ahead of a strong trof of low pressure which will develop over the
Great Plains.  850mb temperatures jump back up to 8-12C by 00Z
Though forecast soundings across the area don`t mix quite that high,
i did bump high temperatures up a little over MOS to try to account
for the good warm advection.  The trof will move into the eastern
Plains and upper Midwest Wednesday night.   A 40-50kt low level jet
develops ahead of the trof over the Mississippi Valley between
06-12Z Thursday, and models show good mass convergence across the
CWFA by 12Z on the nose of this jet in the baroclinic zone.  Start
time of precipitation is still in question, though with all that
convergence over the area by 12Z would think that something should
be moving into the area by then.  Stuck with high chance PoPs in
central and northeast Missouri to account for this after 06Z
Thursday to account for this even though guidance came in a little
drier.  Thursday still looks wet as the cold front pushes through
the area so have maintained likely PoPs across the area.  While
there should be plenty of deep layer shear, widespread severe
weather looks unlikely at this time due to limited heating and
therefore low CAPE values


Carney

.LONG TERM: (Friday through Monday)
Issued at 348 AM CDT Tue Apr 22 2014

Latest runs of the medium range models are in better agreement than
yesterday`s.  The GFS and ECMWF are now pretty darn close with the
cold front from Thursday`s system only making int into central
Arkansas on Friday and then moving back to the north into southern
Missouri by Saturday.  Resulting low level baroclinic zone sets up
across Missouri and by 00Z Sunday a 30+ kt low level jet is pointing
at it.  Both models develop a wide area of moisture convergence
along the baroclinic zone as a result and print out fairly wide
spread precip.  Strong baroclinicity hangs over the area through
Monday with waves of precipitation as a strong negatively tilted
upper level longwave trof moves across the Rockies into the Plains.
This could be a very wet and stormy pattern for Saturday night into
Monday.  However, since these are the first runs I`ve seen to
actually agree fairly well, I haven`t bitten hook-line-and-sinker on
them yet.  That being said I did bump up pops a bit to account for
the better model agreement.  Temperatures will be highly dependent
on where the surface front sets up and how it moves through the
weekend.  Needless to say, the Saturday through Monday time period
is still a low confidence forecast.

Carney

&&

.AVIATION:  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 544 AM CDT Tue Apr 22 2014

Dry, VFR flight conditions will prevail across all TAF sites.
North-northwesterly winds generally between 10-15KT will decrease
after sunset and gradually veer to the northeast by the end of
the forecast period.

Specifics for KSTL:
Dry, VFR flight conditions will prevail through the period, with
northwest winds between 10-15KT decreasing after sunset and
gradually veering to the northeast by Wednesday morning.

JP

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     69  46  70  52 /   0   0   5  10
Quincy          66  42  68  50 /   0   0  10  40
Columbia        68  45  73  54 /   0   0   5  40
Jefferson City  69  43  74  54 /   0   0   5  40
Salem           68  42  67  50 /   0   0   5  10
Farmington      68  41  71  49 /   5   0   0  10

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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